1. Field of the Invention
The present invention relates to a migrating dye, ink or colorant indicator, for example, visually changing paper (VCP) or a time indicator, which provides a rapid and clear indicia of expiration, e.g., change in color of the image, and includes a means for fixating the image produced so that it is not blurred.
2. Description of the Related Art
There are numerous type migrating dye indicators. By the use of the term "dye" herein, it is meant an ink, dye or colorant that can be used to print an indicia and is capable of migrating through a specific media. One type of migrating dye indicator is a time indicator which provides, after activation, a visual indication of the passage of an amount of time. Such a time indicator is useful, for example, as a game piece, as a security badge, as an indicator of the length of time a perishable item has been on the wholesaler's or retailer's shelf and for numerous other uses.
U.S. Pat. Nos. 5,058,088 and 4,903,254, both to Haas disclose the use of migrating dyes to develop an image.
U.S. Pat. No. 5,058,088 describes a time indicator which includes a first substrate having first and second surfaces and at least two indicia areas on the first surface. A second substrate having first and second surfaces is also provided. A first chemical agent is provided on each of the indicia areas and a second chemical agent is provided on the first surface of the second substrate. The first surfaces of each substrate overlay and are in contact with each other, the chemical agents coacting to cause a visually perceptible change at one of the second surfaces overlaying the first indicia area in a first selected time interval and a visually perceptible change in said second surface overlaying the second indicia area in a second selected time interval, the first selected time interval differing from the second selected time interval. A preferred embodiment of the time indicator includes an ink pattern of dots printed in a preselected pattern in the indicia area and an adhesive activator means on the first surface of the second substrate. The ink and activator coact to cause the ink pattern of dots to gradually bleed and blend together to cause a visually perceptible change through the second substrate overlaying the indicia area in a selected time interval. Preferred embodiments of the invention are self-timing parking permits and tickets.
U.S. Pat. No. 4,903,254 describes a time indicator for use as a security badge. The badge includes a four-layer front part and a two-layer rear part. The front part has, overlying each other, a transparent front support layer with a front print display surface, an adhesive and ink display layer with a front ink display surface, an optical barrier layer; and an adhesive and ink dissolver layer. The rear part has, overlaying each other, an ink film layer and a backup member layer. Upon issue of the badge, a release sheet is peeled off the ink film layer, and the front part is overlaid and pressed down upon the rear part, with the adhesive and ink dissolver layer and the ink film layer forming an assembly joint therebetween. The time interval then begins and the ink migrates from the ink film layer, in series, through the assembly joint, the ink dissolver layer, the optical barrier layer, the adhesive and ink display layer to the front ink display surface, where it forms expiration notice words and diagonal voiding bars after expiration to the time interval.
Generally, in the aforedescribed technology, a dye is incorporated into a conventional ink and an image printed on a substrate using any conventional printing method. The migration of the dye is activated by applying an overlay (display layer) onto the printed image, the display layer comprising, for example, a pressure sensitive adhesive on a clear plastic sheet. The adhesive may be clear or opaque (usually white). The dye migrates into the adhesive and is seen by the viewer of the display layer. Multiple colors can be developed by using multiple dyes to provide images, symbols or printed messages.
The original printed image maybe hidden by a confusion pattern, an opaque layer, multiple color inks/dyes or any other method known to one skilled in the art. Confusion patterns can be random or pattern dots of migrating and non-migrating inks.
The image development time can be controlled by several factors such as adhesive composition, selection of dye, adhesive thickness, multiple adhesive/polymer layers, and the original printed image. Adhesive additives, i.e., accelerators, such as plasticizers are added to increase the speed of dye migration. Selection of these additives can have an effect on the speed and the final color.
A problem that generally exists with such migrating dye indicators is that the indicia gradually appears and changes color over a period of time and after the indicia appears there is a continuing migration of the dye causing a blurring of the indicia. It thus becomes difficult to ascertain the completion of the time interval and if it is important to read the indicia it becomes blurred and unintelligible. The adhesive contains the accelerator agents that not only increase the speed of image appearance but also increase the speed of image blurring. What is required for such migrating dye indicator is a technology wherein the indicia does not blur after the period of time has elapsed.
Methods have been devised for use in time indicators for preventing the blurring of the image that appears. For example, U.S. Pat. No. 5,446,705 to Haas describes one such method. A time indicator is provided that changes color or produces an image or information after a specific time interval. The time indicator includes a base substrate with colored dye deposited on a first surface; and a substrate having an adhesive on a first surface thereof, the adhesive positioned at discrete locations on the first surface of the substrate. The substrate and the base substrate are put into adhesive contact. The adhesive contacts and coacts the colored dye to dissolve the dye and permit the dye to migrate through the adhesive to cause a color change visible through the substrate. The discrete adhesive inhibits lateral migration of the dye to preserve the image or information of the dye in a clear and/or understandable condition.
This method, in effect, creates a physical barrier that prevents the unwanted migration of the dye. The barrier contains the dye within a specified area. The dye is prevented from horizontal diffusion through the adhesive by the discontinuous pattern of adhesive (dots). Between the dots is an air barrier that prevents the dye from migrating and blurring the image. The dye diffuses within the individual dots adhesive but does not travel any further.
It is desirable under certain circumstances to retain the resulting migrating dye image or indicia for long periods of time without blurring. This is particularly desirable for hidden messages, game pieces, coupons and promotions that benefit from self appearing messages. It is thus highly desirable, and in fact required for some uses that the migrating dye image appear relatively fast and remain legible after long periods of time, e.g., 6 months.